The present invention relates generally to sharpening the cutting edges on implements such as knives, scissors, arrow broadheads and the like, and more specifically to a hand-held sharpening device for such implements. The present invention can sharpen both single and double-sided cutting edges.
Since the advent of the use of sharpened implements the need to maintain their edge sharpness has led, over the years, to a myriad of devices and methods to accomplish this task. These devices and methods have accomplished this task with varying a degree of success but have shortcomings as discussed below.
Some sharpening devices such that those disclosed in U.S. Pat. No. 4,112,790 to Marder and U.S. Pat. No. 5,377,563 to Weeks use round sharpening elements which, by virtue of their shape, do not produce a true xe2x80x9cVxe2x80x9d-shaped edge desired for durability and improved sharpness.
Other sharpening devices such as that disclosed in U.S. Pat. No. 4,530,188 to Graves utilize an abrasive material for the sharpening elements. With this type of material, it is difficult to obtain an exact profile to impart on the edge to be sharpened and to maintain that profile with repeated use.
Still other devices such as that disclosed in U.S. Pat. No. 6,393,946 to Kenesky fail to efficiently utilize the sharpening elements, requiring replacement of the elements when only a small fraction of the edges available has been used.
A further problem with many existing devices is micro-chipping on the working edge of the sharpening elements. Some occurrences of micro-chipping are attributable to carelessness or improper technique on the part of the user. The proper technique is to draw the implement being sharpened toward the body of the sharpener thereby providing greater rigidity and thus minimizing vibrationxe2x80x94an important factor to prevent micro-chipping. Another significant factor is the shape of the relief for the working edge in a given application. A radial form relief, or in other words a convex shape, provides the greatest strength, as opposed to a straight bevel relief or a concave relief which prove to be not as strong in this type of application. A further significant factor of micro-chipping is the quality of the material being used for the sharpening elements.
In view of the foregoing background, there is a need in the art to provide an improved edge sharpener that is easy to use while promoting the proper sharpening technique; that is easy to adjust for providing a fresh sharpening edge while efficiently utilizing the sharpening elements; that is versatile in the range of implements that can be sharpened; that can consistently provide a suitable sharpened edge; and that is durable.
The present invention provides a simple, durable and inexpensive device for sharpening an edge on a variety of implements. The preferred embodiment of the present invention includes a sharpener body having a removable, ergonomically shaped handle extending therefrom. The sharpener body has a pair of bosses for releasably securing a pair of interchangeable sharpening elements to the head in an angled manner so as to provide a V-shaped opening. The bosses are configured to be received within slots formed in each sharpening element and maintain the pair of sharpening elements in a proper angular relationship to provide a fixed included angle for the V-shaped opening. The implement is passed through the V-shaped opening to sharpen its cutting edge.
In one aspect of the present invention, each sharpening element is configured with a pair of opposite edges designed as the sharpening edges. Each edge is arranged to provide a different included angle. For example, one of the sharpening edges is perpendicular to the axis of movement of the sharpening element to provide an first included angle of about 62xc2x0, while the opposite sharpening edge is canted at approximately 82xc2x0 to the axis of movement to provide a second included angle of about 45xc2x0. The first included angle of 62xc2x0 is suitable for any implement requiring a 60xc2x0 cutting edge included angle since it allows some clearance between the actual cutting edge and the adjacent surfaces of the implement being sharpened. Similarly, the second included angle of 45xc2x0 is suitable for any implement, such as knives, with a cutting edge included angle between 30xc2x0 and 40xc2x0.
In another aspect of the present invention, the sharpening elements are spaced apart from one another so as not to be in contact, thereby allowing incremental and independent positioning of each element by simply loosening its mounting screw and moving it in its slot. Incremental adjustment of each sharpening element allows utilization of the edges of the sharpening elements along a significant portion of their length, thereby providing a fresh portion of the edge without removing the sharpening elements from the body.
In yet another aspect of the present invention, the sharpener body includes an adjuster to achieve a more precise incremental movement of the sharpening elements. In this aspect, the present invention contemplates the use of one adjustable and one fixed sharpening element, but with both elements being removable, or alternately the use of two adjustable sharpening elements.
In still another aspect of the present invention, the geometry of the sharpening elements are optimized for a given application. In this aspect, each sharpening element is provided with a relief, radial in form, to strengthen the edge and reduce the potential for cracking or chipping. Additionally, the sharpening elements have rounded corners to avoid scratching the surfaces, adjacent to its cutting edge, of the implement being sharpened should the implement be accidentally twisted during sharpening.
In a further aspect of the present invention, the sharpener body has a handle releasably secured thereto. The handle may include a flat surface that allows the user to position the sharpener on a table top or other stable surface to facilitate sharpening. The handle may be removed and interchanged to the opposite side of the sharpener body to facilitate either right- or left-hand usage. Further, the handle may be removed and the body attached separately to another device, such as a hunting bow, for convenience of use in the field. In this configuration, a stabilizer may be secured to the free end of the sharpener body.
Further aspects and areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the foregoing aspects of the invention, as well as the following detailed description and specific examples, should not be construed to limit the spirit and scope of the present invention.